A large body of experimental data suggests that activated cellular oncogenes, either acting alone or in combination, may be responsible for at least some human neoplasias. Two major classes of oncogene products are those having tyrosine kinase activity and those located in the nucleus. We have discovered that interactions between pp60c-src, the best studied example of a cellular tyrosine kinase, and the nuclear oncogenes adeno E1A, polyoma large T (plt) and myc can induce transformation NIH 3T3 cells and that gap junctional communication is downregulated by overexpression of pp60c-src and activated mutants. We will transfect sense and antisense plasmids which express the c-src, p27 gap junction protein, E1A, plt, v-myc genes and their mutants into rodent cells and compare the resultant effects on gap junction communication and other biological and biochemical properties to determine: 1) if gap junctional communication is reduced due to phosphorylation and if it is cause or an effect of src-induced transformation. 2) what c-src and E1A functions are involved in cotransformation and the reason the c-src/E1A cotransformed cells are not tumorigenic in vivo. (We will simultaneously extend our study of E1A-mediated induction of sensitivity to cytolysis by tumor necrosis factor.) 3) if the modifications to pp60c-src in plt/c-src and v-myc/c-src cotransformed cells are due to enhanced recombination or altered splicing induced by the nuclear oncogenes. We will map the locations of the modifications induced in pp60c-src and, if altered splicing is involved, determine the sequence of the modified forms by cDNA sequencing. These studies are part of our long term goal to trace the molecular pathways involved in carcinogenesis.